Tire vulcanizing mold

ABSTRACT

There is provided a vulcanizing mold for a tire in which the capacity of venting air through between the molding pieces of the sector mold is significantly enhanced. A tread ring for vulcanizing and shaping a tread of the tire comprises plural sector molds which are separately formed in the circumferential direction so as to be brought into surface contact with each other. Each of the sector molds comprises segments and plural movable molding pieces circumferentially aligned and disposed on the inner surface side of the segment, and each of the movable molding pieces of each sector mold is urged away from each other.

TECHNICAL FIELD

[0001] The present invention relates to a vulcanizing mold for a tire,particularly to improvement in tread ring contributing to vulcanizingand shaping of a tire tread for significantly enhancing the capacity ofventing air in the mold.

BACKGROUND

[0002] For a so-called split mold in which a tread ring comprises pluralsector molds separately formed in the circumferential direction, it iswidely known, as conventional technique for venting air in the mold, toprovide vent holes in the sector molds themselves.

[0003] In this technique, the rubber penetrates into the vent holes toyield whisker-like spews which spoils the appearance of the tire therebyrequiring a special processing step for cutting and removing a number ofspews. Thus, as shown in FIG. 1 by way of example, it is recentlyproposed to vent air through minute gaps δ between plural fixed moldingpieces 22 which are provided on an inner surface side of each sectormold 21 and are circumferentially aligned with each other. In this case,it is considered to be advantageous to improve the capacity of ventingair, that vacuum suction means are connected to the minute gaps for aforced ventilation.

[0004] In the conventional technique in which air is vented throughbetween the fixed molding pieces 22, however, the piece gaps δ are setto be a small given value so as to prevent the rubber from flowing outand hence the capacity of venting is lower than that of venting air bymeans of the vent holes, which tends to cause a drawback in theappearance such as bares. This drawback cannot be thoroughly solved dueto the piece gaps being too small even though the forced ventilation iscarried out by the vacuum suction means.

[0005] Further in this case, since the rubber penetrates into the piecegaps δ and hence the gap δ is plugged in the early stage to lower thecapacity of venting air, there is a problem that cleaning the mold at ashort cycle is inevitable.

[0006] The present invention is aimed to solve the above-mentioneddrawback of the conventional technique, and an object thereof is toprovide a vulcanizing mold for a tire in which the capacity of ventingair through between the molding pieces of the sector mold issignificantly enhanced to eliminate a possibility of causing thedefective appearance such as bares even though almost all or all of thevent holes is removed.

DISCLOSURE OF THE INVENTION

[0007] A vulcanizing mold for a tire according to the present inventionhas a tread ring for vulcanizing and shaping a tread of the tire, thetread ring comprising plural, such as six to eighteen, sector moldswhich are separately formed in the circumferential direction so as to bebrought into surface contact with each other, wherein each of the sectormolds comprises arched segments and plural, such as four to eight,movable molding pieces circumferentially aligned with each other anddisposed on the inner surface side of the segments, and wherein themovable molding pieces of each sector mold are urged away from eachother by a spring member, actuator or the like.

[0008] In the vulcanizing mold according to the present invention, themovable molding pieces are largely spaced with each other by thepressing action of the spring member or the like in its open position inwhich the sector molds are spaced with each other.

[0009] Meanwhile, when each of the sector molds is displaced in theradially inward direction to close the vulcanizing mold and the movablemolding pieces of the adjacent sector molds contact with each other,each of the movable molding pieces of the sector molds is displacedclosely with each other against the pressing force of the spring or, forexample, under an inactive state of the actuator and these moldingpieces have approached with each other to a predefined small gap at thepoint of a complete closing position being reached.

[0010] Therefore, in the present invention, when a green tire is shapedand vulcanized, the efficiency of venting air can be significantlyenhanced by venting air in the mold through between molding pieceshaving wider clearance until the vulcanizing mold is in a completeclosing position, usually after the movable molding pieces of theadjacent sector molds contact with each other and before each of themovable molding pieces in the sector molds approaches with each other tothe predefined small gaps, thereby effectively preventing formation ofbares or the like without providing few or no vent holes. Suchenhancement is particularly outstanding in the case where air isforcibly vented through the predefined small gaps of the molding pieces.

[0011] More preferably, in such a vulcanizing mold, a relative clearanceof the movable molding pieces is less than 0.05 mm in a position inwhich the sector molds form the tread ring or, in other words, in acomplete closing position. Thus, the clearance is 0.05 mm or more in aposition in which the sector molds are spaced with each other or, alsoin other words, in a opening position.

[0012] The former allows air to be vented while the rubber is preventedfrom flowing out. The latter can realize smooth and effectiveventilation of air.

BRIEF DESCRIPTION OF DRAWINGS

[0013]FIG. 1 is a schematic diagram showing a conventional sector mold;and

[0014]FIG. 2 is a schematic diagram showing an embodiment according tothe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0015] In an embodiment of the present invention shown in the FIG. 2,the reference numeral 1 designates a sector mold.

[0016] In this embodiment, a tread ring is composed of a total of, forexample, eight sector molds 1 in a closing position. Each of the sectormolds 1 comprises a segment 2 having a arched shape and, for example,four molding pieces 3 circumferentially aligned with each other anddisposed on the inner surface side of the segments 2 to be able to movealong a arched face. The molding pieces 3 of the sector molds are urgedaway from each other by a spring member 4 mounted therebetween.

[0017] In this case, each of adjacent molding pieces 3 is specified itsspacing limit location by a not-shown stopper or the like and themaximum spacing distance is, for example, 0.5 mm, so that there is nopossibility of each molding piece 3 being excessively displaced to fallaway from the segment 2.

[0018] In a opening state of the vulcanizing mold or, directly, thesector molds 1 as shown in FIG. 2(a), each of the molding pieces 3 ofthe sector molds 1 is in the spacing position up to the limit locationand each of the molding pieces 3 between the sector molds is also in thespacing position.

[0019] On the contrary, when each of the sector molds 1 is displacedradially inwardly, as shown by the arrow A in the figure, by closing themold for vulcanizing and shaping a green tire, each of the moldingpieces 3 between the adjacent sector molds tightly contacts with eachother. Then, the clearances between the molding pieces 3 in the sectormolds become smaller. Finally, the sector molds 1 form a tread ring 5 asshown in FIG. 2(b) at the completion of closing the molds and each ofthe molding pieces 3 in the sector molds is aligned with a clearance ofless than 0.05 mm, which is the predefined gap.

[0020] Hence, the embodiment can significantly enhance the efficiency ofventing air as compared with the prior art by venting air in the moldthrough between the molding pieces having wider clearances especiallyafter each of the molding pieces 3 of the adjacent sector molds 1tightly contacts with each other and before the completion of closingthe mold. This is more effective when air is forcibly vented by means ofvacuum suction.

[0021] Moreover, with using this mold, the clearance of the moldingpieces becomes larger while opening the mold, so that the rubber can beeffectively prevented from sticking between the molding pieces to assurethe performance of venting air for a long period.

INDUSTRIAL APPLICABILITY

[0022] As having been clearly shown in the above description, accordingto the present invention, the capacity of venting air can besignificantly improved owing particularly to the large clearances of themolding pieces of each sector mold, so that the formation of bares orthe like can be effectively prevented even though almost all or all ofthe vent holes is eliminated.

[0023] In addition, the rubber is prevented from sticking between themolding pieces to assure the performance of venting air for a longperiod, so that a cycle of cleaning the mold can be largely extended,which enhances an operation efficiency of the mold.

1. A vulcanizing mold for a tire, comprising a tread ring forvulcanizing and shaping a tread of the tire, the tread ring comprisingplural sector molds which are separately formed in the circumferentialdirection so as to be brought into surface contact with each other,wherein each of the sector molds comprises segments and plural movablemolding pieces circumferentially aligned with each other and disposed onthe inner surface side of the segments, and wherein the movable moldingpieces of each sector mold are urged away from each other.
 2. Thevulcanizing mold for a tire according to claim 1, wherein a relativeclearance of the movable molding pieces is less than 0.05 mm in aposition in which the sector molds form the tread ring.